Networks have been widely used these days as in the use of the Internet and the structures of LANs (local area networks). The wide use of broad-band communications has been started, which is expected to be easier to use than networks.
In these situations, it has been proposed that not only computers but various electronic units are connected to a network to configure a system.
When various AV (audio visual) units are connected to a network, for example, various AV contents uploaded through the Internet can be easily taken and viewed or listened to as they are by streaming reproduction on television receivers and audio amplifiers, and can be recorded by VTRs, without using personal computers.
To configure such a network system, it is necessary for commercially available units, such as the above AV units, to have a structure capable of being connected to a network.
In the current condition, however, many commercially available AV units have structures serving as so-called stand alone units, in the viewpoint of network connections. In other words, since they are not designed for use in networks, they do not have structures, including hardware structures, which can be connected to a network.
For example, since media such as CDs and DVDs and digital VCRs (video cassette recorders) have been spread, audio and visual sources to be recorded in the media have digital-signal formats. Because AV units handling the media are currently not designed for use in networks, the AV units handing the media mainly use analog signals for inputting and outputting AV sources.
AV units capable of performing data communications by the use of IEEE 1394 and others as a data interface standard have also been proposed. What the data interface implements is, however, mainly editing such as dubbing between AV units, for example, and is not network connections to the Internet and others according to a communication protocol such as TCP/IP. A network architecture called HAVi, which is based on IEEE 1394, has also been proposed, but it does not solve a problem in IEEE 1394 to implement network connections.
Therefore, although networks have been spread, there still exist many commercially available non-networked units, such as the above-described AV units, and they cannot be used in network environments.